1. Field of the Invention
This invention relates a method for producing a connecting tube that interconnects the shaft and the handle of a racket, more particularly to a method for producing a connecting tube that interconnects the shaft and the handle of the racket, which method can reduce the defective ratio of the connecting tube.
2. Description of the Related Art
Rackets, such as badminton rackets, tennis rackets, etc., have connecting tubes which interconnect the shafts and the handles of the rackets. The connecting tubes are manufactured in the following manner. FIGS. 1(A) to 1(F) are schematic views illustrating a conventional method of producing the connecting tube which interconnects the shaft and the handle of the racket. Impregnated fiber laminates are rolled into a tubular internal wall (1), as shown in FIG. 1(A). A foamable material (2), which has not expanded, is provided around the tubular internal wall (1) at a predetermined position, as shown in FIG. 1(B). A predetermined number of impregnated fiber laminates (3) are then wrapped around the foamable material (2) in order to form an external wall, as shown in FIG. 1(C). The wrapped tubular internal wall (1) is disposed in a mold (4) with a mold cavity (4a), as shown in FIG. 1(D). The mold (4) is heated in order to allow the foamable material (2) to expand into a rigid foam (2a) and depress the impregnated fiber laminates (3) to fill the mold cavity (4a) in order to form an external wall, as shown in FIG. 1(E). A connecting tube 5 is thus obtained, as shown in FIG. 1(F).
However, since it is difficult to control the expanding ratio of the unexpanded foamable material (2) and the amount of the unexpanded foamable material (2) around the tubular internal wall (1), the foamable material (2) will depress the tubular internal wall (1) inwardly during the heating process, thereby causing the tubular internal wall (1) to deform irregularly and causing the thickness (S) of the tubular internal wall (1) and the external wall to be uneven, as best illustrated in FIGS. I(F), 2(A) and 2(B). This will reduce the strength of the racket and increase the defective ratio of the racket.